Webflow’s built-in scroll interactions aren’t tied to a general/arbitrary up/down scroll function in the manner in which you need. You can scroll things in/out of view based upon another element in the dom, but not directly tied to a scroll action in a general sense. I don’t know the proper term for this, an experienced javascript/jquery developer could probably do a better job of explaining the details of it.
Just insert the full minified popr.js script directly in the “Footer Code” section of your site settings (it’s only 12 lines of code, 2KB - wrap it in script tags). That would probably be the easiest way, then you can set the options for the speed/mode directly in the script. Then include their CSS styles in the “Head Code” section of your site (wrapped in style tags)
You will then re-create their HTML structure inside Webflow, and attach the necessary classes… just follow the directions on the scripts homepage. You can even set your options via data attributes inside the Webflow designer if preferred. The default styling provided by the included CSS with the plugin is pretty basic, just like your Pulse example you provided - but I’m sure you could even tweak/override that rather easily once you get into it a bit.
No problem… I left out one step above, don’t forget to actually call the plugin as well after you have included it in the Footer Code section. Do this directly below the actual minified popr.js script… This portion of code included below, this piece already has the options set for the position (top) and speed (300ms)…